I'm the lead developer of TortoiseSVN. I joined the project in the very early stages when it wouldn't even compile yet, and I've been working on it ever since.
Some people wonder why I would work for free on an open source project, while I could have made a lot of money if I would have created a closed source project and would sell the program.
Well, sure I wish I could make a living by working on this project. But I don't think that's ever going to happen. And still, I'm working on this project almost every day for several hours. So what's driving me to do this?
It's the feedback of the community, the appreciation I get from those who post on the mailing list, the discussions about problems and how to improve the UI. Here, people appreciate what I do, even if they don't always agree with my decisions. So that's why I like working for free on this project.